Van Middledyk's work was the first major historical study of Puerto Rico in English. Van Middledyk advanced Puerto Rican historiography by building on the works of Brau, Coll y Toste, and Acosta, and by consulting early Spanish chronicles. A librarian at the Free Public Library of San Juan, Van Middledyk possessed knowledge of and access to considerable primary source material. His history is sympathetic to the Indians and highly critical of Spanish colonial administration. Coming in the wake of American military occupation, the book sought to explain and justify control of the island by the United States.